powerpc: Clear RI and EE at the same time in system call exit
PATCH 1/1 powerpc: Clear RI and EE at the same time in system call exit
In system call exit we currently clear RI and EE separately. An mtmsrd is a slow operation and we can save cycles by doing it all in one go.
This does complicate things a bit - we have to be careful to restore RI if we branch out before returning to userspace.
On a POWER7 with virtual cputime disabled this patch improves the null system call by 7%.
---
arch/powerpc/kernel/entry_64.S +11 -12
@@ -197,7 +197,16 @@ syscall_exit: wrteei 0 #else ld r10,PACAKMSR(r13) - mtmsrd r10,1 + /* + * For performance reasons we clear RI the same time that we + * clear EE. We only need to clear RI just before we restore r13 + * below, but batching it with EE saves us one expensive mtmsrd call. + * We have to be careful to restore RI if we branch anywhere from + * here (eg syscall_exit_work). + */ + li r9,MSR_RI + andc r11,r10,r9 + mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ ld r9,TI_FLAGS(r12)
@@ -214,17 +223,6 @@ BEGIN_FTR_SECTION END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS) andi. r6,r8,MSR_PR ld r4,_LINK(r1) - /* - * Clear RI before restoring r13. If we are returning to - * userspace and we take an exception after restoring r13, - * we end up corrupting the userspace r13 value. - */ -#ifdef CONFIG_PPC_BOOK3S - /* No MSR:RI on BookE */ - li r12,MSR_RI - andc r11,r10,r12 - mtmsrd r11,1 /* clear MSR.RI */ -#endif /* CONFIG_PPC_BOOK3S */ beq- 1f ACCOUNT_CPU_USER_EXIT(r11, r12)
@@ -271,6 +269,7 @@ syscall_enosys: b syscall_exit syscall_exit_work: + mtmsrd r10,1 /* Restore RI */ /* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr. If TIF_NOERROR is set, just save r3 as it is. */
Quoted 55 lines · Anton Blanchard
In system call exit we currently clear RI and EE separately. An mtmsrd is a slow operation and we can save cycles by doing it all in one go.
This does complicate things a bit - we have to be careful to restore RI if we branch out before returning to userspace.
On a POWER7 with virtual cputime disabled this patch improves the null system call by 7%.
Signed-off-by Anton Blanchard <[email protected]>---
Index:
linux-build/arch/powerpc/kernel/entry_64.S
===================================================================arch/powerpc/kernel/entry_64.S +10
-12@@ -197,7 +197,16 @@ syscall_exit: wrteei 0 #else ld r10,PACAKMSR(r13) - mtmsrd r10,1 + /* + * For performance reasons we clear RI the same time that we + * clear EE. We only need to clear RI just before we restore r13 + * below, but batching it with EE saves us one expensive mtmsrd call. + * We have to be careful to restore RI if we branch anywhere from + * here (eg syscall_exit_work). + */ + li r9,MSR_RI + andc r11,r10,r9 + mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ ld r9,TI_FLAGS(r12)@@ -214,17 +223,6 @@ BEGIN_FTR_SECTION END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS) andi. r6,r8,MSR_PR ld r4,_LINK(r1) - /* - * Clear RI before restoring r13. If we are returning to - * userspace and we take an exception after restoring r13, - * we end up corrupting the userspace r13 value. - */ -#ifdef CONFIG_PPC_BOOK3S - /* No MSR:RI on BookE */ - li r12,MSR_RI - andc r11,r10,r12 - mtmsrd r11,1 /* clear MSR.RI */ -#endif /* CONFIG_PPC_BOOK3S */ beq- 1f ACCOUNT_CPU_USER_EXIT(r11, r12)
arch/powerpc/kernel/entry_64.S syscall_enosys: · line 272
Quoted 4 lines
arch/powerpc/kernel/entry_64.S +1
-0@@ -271,6 +269,7 @@ syscall_enosys: b syscall_exit syscall_exit_work: + mtmsrd r10,1 /* Restore RI */
That mtmsrd needs an #ifdef CONFIG_PPC_BOOK3S
-Scott
PATCH 1/1 powerpc: Clear RI and EE at the same time in system call exit
Hi Scott,
Quoted 4 lines
Review
Quoted 2 lines
syscall_exit_work:(quoted diff) +1
-0+ mtmsrd r10,1 /* Restore RI */That mtmsrd needs an #ifdef
CONFIG_PPC_BOOK3S
Thanks!
Anton
--
In system call exit we currently clear RI and EE separately. An mtmsrd is a slow operation and we can save cycles by doing it all in one go.
This does complicate things a bit - we have to be careful to restore RI if we branch out before returning to userspace.
On a POWER7 with virtual cputime disabled this patch improves the null system call by 7%.
---
arch/powerpc/kernel/entry_64.S +13 -12
@@ -197,7 +197,16 @@ syscall_exit: wrteei 0 #else ld r10,PACAKMSR(r13) - mtmsrd r10,1 + /* + * For performance reasons we clear RI the same time that we + * clear EE. We only need to clear RI just before we restore r13 + * below, but batching it with EE saves us one expensive mtmsrd call. + * We have to be careful to restore RI if we branch anywhere from + * here (eg syscall_exit_work). + */ + li r9,MSR_RI + andc r11,r10,r9 + mtmsrd r11,1 #endif /* CONFIG_PPC_BOOK3E */ ld r9,TI_FLAGS(r12)
@@ -214,17 +223,6 @@ BEGIN_FTR_SECTION END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS) andi. r6,r8,MSR_PR ld r4,_LINK(r1) - /* - * Clear RI before restoring r13. If we are returning to - * userspace and we take an exception after restoring r13, - * we end up corrupting the userspace r13 value. - */ -#ifdef CONFIG_PPC_BOOK3S - /* No MSR:RI on BookE */ - li r12,MSR_RI - andc r11,r10,r12 - mtmsrd r11,1 /* clear MSR.RI */ -#endif /* CONFIG_PPC_BOOK3S */ beq- 1f ACCOUNT_CPU_USER_EXIT(r11, r12)
@@ -271,6 +269,9 @@ syscall_enosys: b syscall_exit syscall_exit_work: +#ifdef CONFIG_PPC_BOOK3S + mtmsrd r10,1 /* Restore RI */ +#endif /* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr. If TIF_NOERROR is set, just save r3 as it is. */